Abstract: A system comprising a heat generating load, a power control element for controlling power supply to the heat generating load, a temperature detecting circuit for producing an ON signal when the temperature of the load detected by a temperature sensor is lower than a set temperature and an OFF signal when the temperature has reached the set temperature, and a control circuit for feeding on ON or OFF signal to the power control element in response to the signal from the temperature detecting circuit. The control circuit includes a hysteresis control circuit which, once the temperature detecting circuit detects that the temperature has reached the set temperature, permits the power control element to receive OFF signals for a suitable period of time even after the temperature has subsequently lowered to a level at which the signal from the temperature detecting circuit changes to an ON signal.